ACTION OF FLUORIDE ON TEETH

ACTION OF FLUORIDE ON TEETH

It is deposited on the enamel by the formation of a globular deposits of CaF2.

These globules do not dissolve as quickly as expected on their basis of their solubility.

The solubility is attributed to prescence of phosphate and proteins rich surface covering these globules.

The dissolution of fluoride from globules is pH dependent,because phosphate ions are released when they are protonated at low pH.

During a cariogenic challenge, F released from this globules may diffuse into the enamel promoting reformation of apatite.

It is known that the formation of the CaF2 reservoir is increased under acidic compared to neutral condition.

Fluoride from saliva or exogenous sources such as fluoride rinses, gels, varnishes and toothpastes is taken up preferentially by biofilms, lessens the effects of an acidogenic challenge and facilitates remineralization when the resting pH returns to 7.0.

INCREASED CONCENTRATION

Increased concentrations of calcium and phosphate in biofilms, saliva and artificial calcifying fluids, excessive levels of fluoride lead to rapid mineral precipitation on the enamel surface and owing to occlusion of surface porosities communicating with the subsurface leads to white-spots.

So that high concentration topical fluoride results in unsightly white opacification of enamel lesions.

High frequency application of low F concentration agents has been considered the most beneficial treatment regime.

journal of de n t i s t r y, 2 0 0 8

Adv Dent Res ,1994

FLUORIDE MECHANISM

FLUORIDE
Fluoride ions promote the formation of fluorapatite in enamel in the presence of calcium and phosphate ions produced during enamel demineralization by plaque bacterial organic acids.

Fluoride ions can also drive the remineralization of previouslydemineralized enamel if enough salivary or plaque calcium and phosphate ions are available.

availability of calcium and phosphate ions can be the limiting factor for net enamel remineralization to occur

this is highly exacerbated under xerostomic condition.

FLUORAPATITE

when the fluoride is applied, for every two fluoride ions, 10 calcium ions and six phosphate ions are required toform one unit cell of fluorapatite (Ca10(PO4)6F2)..

Fluoride mechanisms

1) Free fluoride ion combines with H+ to produce hydrogen fluoride, which migrates throughout acidified plaque.

This ionized form is lipophilic and can readily penetrate bacterial membranes.

Bacterial cytoplasm is relatively alkaline, which forces the dissociation of H+ and F-.

Fluoride ion inhibits various cellular enzymes (enolase, proton extruding ATPase)key to sugar metabolism.

Hydrogen ions simultaneously acidify the cytoplasm, thus slowing cellular activities and inhibiting bacterial function


2) Fluoride integrated in the enamel surface (as fluorapatite, FAP) makes enamel more resistant to demineralization than HAP during acid challenge.

FLUORAPATITE formed is less soluble,this is due to incorporation of fluoride and carbonate is washed out (Tencate).



3) Fluoridated saliva not only decreases critical pH, but also further inhibits demineralization of the deposited CaF2 at the tooth surface.

DCNA,1999
Australian Dental Journal,2008